NaAlNb(PO4)3 NASICON-type phosphate with the Nb5+/Nb4+/Nb3+ multielectron redox activity on sodium intercalation

The NASICON-structured NaAlNb(PO₄)₃ phosphate was synthesized via Pechini sol–gel technique. Electrochemical measurements in sodium half-cells have disclosed that NaAlNb(PO₄)₃ can reversibly intercalate 2Na⁺ ions per formula unit owing to the Nb⁵⁺/Nb⁴⁺/Nb³⁺ multielectron redox processes, which was confirmed by the Nb K-edge XANES measurements. Differential thermal calorimetry has revealed an excellent thermal stability of the sodiated NaAlNb(PO₄)₃/C electrode material up to the point of electrolyte decomposition.